Method and electrolyte for electrodepositing a gold-arsenic alloy

ABSTRACT

AN AQUEOUS ELECTROLYTE SOLUTION HAVING A PH FROM 5.5 TO 8 FOR DEPOSITING HARD, DUCTILE AND BRIGHT ARSENIC CONTAINING GOLD HS BEEN PROVIDED, BESIDES THE VARIOUS BUFFERS AND ALKALI GOLD CYANIDE, COMPLEX AA THIO SULFATE IS ADDED TO FACILITATE THE PROPER INCLUSION OF ARSENIC IN THE GOLD DEPOSIT, SALT COMPOSITION SUITABLE FOR OBTAINING AQUEOUS ELECTROLYTES, A MEHTOD FOR DEPOSITING THE ARSENIC GOLD, TE GOLD ALLOY, AND ELECTRICAL DEVICES HAVING THE ARSENIC GOLD DEPOSIT ON A SURFACE OF THESE DEVICES HAVE ALSO BEEN DISCLOSED.

United States Patent Office 3,753,874 Patented Aug. 21, 1973 3,753,874METHOD AND ELECTROLYTE FOR ELECTRO- DEPOSITING A GOLD-ARSENIC ALLOYRichard Henry Zimmerman, Palmyra, and Richard Lee Brenneman, Camp Hill,Pa., assignors to AMP Incorporated, Harrisburg, Pa.

No Drawing. Continuation-impart of abandoned application Ser. No.807,105, Mar. 13, 1969. This application Dec. 21, 1971, Ser. No. 210,609

Int. Cl. C23b /42 US. Cl. 204-43 G 28 Claims ABSTRACT OF THE DISCLOSUREAn aqueous electrolyte solution having a pH from 5.5 to 8 for depositinghard, ductile, and bright arsenic containing gold has been provided;besides the various buffers and the alkali gold cyanide complex, a thiosulfate is added to facilitate the proper inclusion of arsenic in thegold deposit; salt compositions suitable for obtaining aqueouselectrolytes, a method for depositing the arsenic gold, the gold alloy,and electrical devices having the arsenic gold deposit on a surface ofthese devices have also been disclosed.

This application is a continuation-in-part of application Ser. No.807,105, filed Mar. 13, 1969, and now abandoned.

This invention relates to an improved method of electro depositing goldon electrical devices, such as gold plating electrical conductors, anovel electrolyte used in practicing the method of electro depositinggold as well as a novel salt composition for use in an electrolytesolution or bath. Electrical devices improved with electro depositedgold thereon according to the present invention are within the scope ofthis invention.

A wide variety of electrolytes are used as solutions for plating goldtherefrom. As it is well known, electrolyte solutions used for thispurpose are generally classified in three types based on a pH scale. Thefirst type is an alkaline electrolyte solution. This electrolytecontains gold as potassium gold cyanide in solution and additionalamounts of potassium and sodium cyanide. Electroplating .from a bathoperating with this solution is carried out at a pH of 8 and higher.

As a second type, an acid gold electrolyte solution is well known. Itcontains gold in a form of complex cyanides, and it has additional saltsdissolved in the solution. These salts are derived from organic acidssuch as citrates, acetates, lactates, etc. Electro depositing from thisbath is carried out at a pH below 6.

As a third type of electrolyte solution, a neutral gold electrolyte isemployed. It is a buffered solution whose pH level is kept from 6 to 8.Although it is not truly a neutral" bath over this pH range, it has beendesignated as such in the art.

A number of variations are known of these three basic electrolyte bathcompositions. For example, additives used as complexing agents are oftenemployed. While these additives oifer a solution to certain problems,these same additives, together with the gold salts, cause otherproblems.

A very complex and as yet poorly understood electrochemical interactionof the additives with each other is the reason for a wide variation inresults. Further, not only dissolved gold containing salts whichinteract with the additives but also the variation in the anodic andcathodic reactions, as these occur in the bath, produce differentresults. These various phenomena render the chemistry of electroplatinggold from an electrolyte solution an art with predictability being verydifiicult, if not impossible.

Hence, when the electrolyte components are changed or substituted, manybalancing considerations apply where sacrifices in one variable must bemade .for a gain in another variable. However, these balancingconsiderations are invariably empirical. As an electrolyte bath consistsof a number of components, the permutations and combinations and theeffects of each additive on the electrolyte behavior and the obtainedproduct are manifold; and consequently, the outcome is unpredictable inthe method of plating and the final product. Hence, the plating outcome,while often acceptable in one respect, is completely unacceptable insome other respect.

Further, as it is well known, various electrolytes or baths basedthereon can only be operated over a narrow temperature, pH, and setdissolved salt composition range, as the variations in these may causegold to be reduced and precipitated from the bath solution. Stillfurther, in operating the bath, unwanted products are formed from traceimpurities in the electrolyte; these impurities interact with theelectrolyte and/or the gold being electro deposited such as formingalloys or becoming occluded in the electro deposited gold.

These impurities often interact with a base metal or the electroformedgold in the operating environment to which the gold plated device is tobe subjected. As a consequence, the end product, while initiallyacceptable in appearance, fails in one or more of the basic requirementswhich are hardness, ductility, wear, continuity of film or porosity,oxidation resistance, along with other characterizing properties used toevaluate electro deposited gold and which measure the quality of thedeposited layer on an electrical conductor and/ or deposit such asconductivity of the composite, coloration, density, smoothness, purity,nobility, cycling ability, etc.

When gold in various compositions is deposited from an electrolyte suchas in a standard electrolyte bath such as when employing a rack or abarrel method, or when gold is deposited selectively such as whenemploying a strip line, jet or belt method, generally it deposits in twocrystalline forms. In the so-ealled alloyed gold, i.e. containingco-deposited additives, the form is typically laminar with the laminaeor striations of the crystals parallel to the base on which it isdeposited and visible at magnifications of about to 200 times. With highpurity golds a columnar form is more typical with the crystals formingcolumns perpendicular to the base on which it is deposited, visible atabout the same magnification. More rarely, gold deposits in a randomcrystalline form and still more rarely in a random, fine grainedcrystalline form.

Laminar and columnar gold crystals are formed from the conventionalelectrolytes, and these forms are fairly well known; however, it isimpossible to predict when fine grained, bright, randomly orientedcrystals will be formed from "an electrolyte solution and whatelectrolyte solution will produce bright, ductile, hard, randomlyoriented, fine grained crystals. Moreover, it is substantiallyimpossible to predict when the fine grained crystals will form brightgold.

For the above reasons, the compounding of suitable salts and the use ofthese in an electrolyte bath in terms of the bath eiiiciency and finalproduct properties is still an art beyond routine results achievablewith conventional electrolytes suitable for gold plating, e.g. the finegrained gold electrodeposit. Thus, the evaluation of any novelelectroplating bath composition must be based on the electrolytecomposition, the method of employing the novel electrolyte bath, andphysical properties of the electroformed gold and products madetherefrom, any of which may result in a novel combination in itself.

In accordance with the present invention, a novel electrolyte saltcomposition has been found. This salt composition consisting of theherein defined components or ingredients is suitable for formation of anelectrolyte solution which, in turn, is suitable for depositing goldfrom an electrolyte solution. This electrolyte salt composition whendissolved and used in an electrolyte solution within the defined neutralpH range of 5.5 to 8 under electro deposition conditions has resulted ina novel method for depositing gold, characterized by high efficiencies,fast plating times, and absence of detrimental side reactions; and moreimportantly, the salt composition when so used produces a novel electrodeposited or formed gold product, novel articles of manufacture based onthe novel electro deposited or formed gold, which articles possessexceptionally advantageous properties, such as brightness, hardness,e.g. up to 260 Knoop units, foil strength, ductility, wear, smoothness,solderability, etc. These properties in the final product are achieveddespite the presence of a heretofore unwanted component, i.e. arsenic,in the plating bath which component in fact is now incorporated in theelectro deposited gold layer by means of a heretofore not employedcomplexing agent.

Thus, according to the invention, an electro deposited or formed goldhas been obtained which is bright, hard and ductile and which consistsof randomly oriented, fine grain crystals. This gold displaysbrightness, hardness, and ductility properties, to name only a few,which properties are contributed by the co-deposited arsenic, the lastfrom the electrolyte solution under electro deposition conditions ofparticular kind via a particular complex, e.g. thio-arsenic (III)complexes and/or tris (thio sulfato) arsenic (III).

The above-mentioned arsenic complexes contribute to the unexpectedresults in a manifold manner. First, these complexes elevate thereduction potential with all the attend-ant advantages, and second, thecomplexes prevent the oxidation of As+++ to As+++++. Moreover, whenusing these complexes, the electroplated or electrodeposited goldpossesses the exceptional properties previously mentioned.

Suitable thio or thio sulfato arsenic complexes are those formed fromarsenic and a thio compound such as thio urea; thio chrysine, etc.;further tris (thio sulfato) arsenic complexes formed from precursorssuch as alkali thio sulfates, e.g., sodium thio sulfate and arsenic,etc. Of these arsenic complexes, the tris (thio sulfato) group, such asalkali thio sulfate, is by far the most preferred one and is one whichproduces eminently superior results. The arsenic complexes suitable foruse must be soluble or solubilizable in the electrolyte at the operatingconditions.

Without espousing any theory, these complexes contribute to theelectrolytic deposition reaction by possibly some catalytic action,perhaps by providing arsenic in a form which does not escape as anarsine gas but rather provides arsenic as an alloy forming componentunder proper temperature and current density conditions. It is believedthat 0.1 to 0.9% of weight of arsenic in the gold obtained from anelectrolyte solution by electro deposition or electroforming in thespecified manner produces a novel form of crystalline gold as evidencedby many of the physical and chemical characteristics of this product asfurther descussed herein.

For example, the hardness of a gold foil produced according to the novelmethod when measured in Knoop units at 25 gram load shows a range of 190to 250, which hardness, together with the exceptional brightness andductility has heretofore not been obtained.

Further, the Tafel slope of the novel electro deposited or formed goldis almost equivalent to pure gold when measured against pure goldelectrodes in a 0.1 molar ammonium chloride solution used in this test.

The above properties such as brightness are exceptionally well displayedwhen the amount of arsenic in the electro deposited gold is 0.1 to 0.5percent by weight and when the deposition is properly carried out. Inthe deposit, the balance is gold with trace impurities normallyassociated with electro deposition of gold. As the amount of arsenicincreases in the gold deposit, the properties also vary; for example, atconcentrations above 0.9% by weight, the grain structure starts tochange, and at about 1.0% by weight of arsenic, crystal structure tendstowards the columnar type.

Consequently, on the basis of the amount of arsenic by weight and thecrystalline structure, the present electro deposited gold can bedelineated from the prior art electro deposited gold such as by grainstructure, brightness, hardness and ductility. Although other finegrained, crystalline gold forms have been observed, these are neitherbased on arsenic nor as bright and hard nor ductile at the hard nesslevels herein nor as noble when compared for polarization behavior inrespect to slope characteristics based on Tafel equation, i.e. Tafelslope.

Surface smoothness of the novel gold deposits is also exceptional. In anelectron microscope at a magnification of 32,000 times and aphotographic enlargement of up to 80,000 times, these deposits appearexceptionally smooth based on the definition employed in the art.

Additional, exceptional properties of the novel gold deposits which arebased mostly on performance are abrasive resistance, wearability in useof a gold plated article, oxidation resistance, easy wettability forsoldering, capability of forming thick electro deposits, and goodthrowing power, e.g. 37% as determined in a Haring cell.

In reference to electrical contacts having on the contact surfaces thenovel electro deposited gold, the prod uct specifications govern thesedevices for their acceptability. Specific geometries employed for thespecific contact devices have characteristic wear cycles. Whenelectrical devices are compared which have contact surfaces plated withthe novel gold deposits to the devices plated with gold having a similarhardness produced from a commercially available electrolytic formulationcontaining gold, cobalt, and indium, it has been found that onstatistical bases the same connectors which have previously been barrelplated with the novel gold deposit have outlasted and outperformed thesimilarly plated prior art connectors after repeated work cycling(insertionwithdrawal), e.g. when measured at initial lower level contactresistance and rated current resistance and after 250 to 500 work cyclesat 1 and 2.5 milliamps DC. and 5 amps A.C. At the same time the novelgold plated connectors have out-performed the prior art platedconnectors based on the same test after repeated work cycling and whenmeasured as final contact resistance for durability and corrosion afterrepeated temperature cycling.

Improved results based on these tests bespeak the ability of theconnectors to perform especially in low voltage level circuitry forextended periods of time. Other equally important properties which thenovel gold plated connectors possess are: crimpability, i.e. it relatesto ductility; scratch resistance; gold deposit porosity; chemicalresistance; excellent solderability, etc. The last property is measuredby means of a dip method comparing solder covered area and solder barearea; it can also be measured by ease of spreading of a certain amountof solder and the surface area which a certain amount covers and thecontact angle of this solder with the plated surface.

If the novel electro deposited gold is used to produce heavy deposits,it still displays the fine crystalline structure which is ratherunexpected. It is also rather unexpected that while commonly employedhardening and brightening agents normally tend to produce an oxide filmTABLE I.-ELECTROLYTE BATH COMPOSITION Weight of components per unitvolume of water Electrolyte bath components G./l. Oz./gal.

Monobasic otassium phosphate 60 to 120 8 to 16.

(KHzPOfi.

Potassium citrate (K CaH O H20) 60 to 120 Do sequestering agent; such asdisodium .25 to 1.0 0.033 to 0.132.

ethylenediaminetetraacetate dihydrate (NaZEDTAQH O).

Gold as potassium gold cyanide [KA11(CN)2] (the amount used is on basisof elemental gold).

10.7 to 14 1.3 to 1.5 tr.

Trivalent arsenic as sodium arsenite .02 to .2 .0026 to .026.

(NaAsOz) (the amount used is on basis of elemental arsenic).

As complexing agent therefor, sodium 5 to 0.66 to 1.32.

In a bath solution used herein, the total quantity of the specifiedamounts of each component is added per unit volume of the wateraccording to the units employed. The sequestering agent is an optionaladditive and is employed as a safeguard against contamination.

Generally, a number of sequestering agents may be used. Of these agentsethylene diamine tetraacetate is most often used; and as a result of theprevalent use of this compound, any of the other sequestering agents andthe amounts of the same in electrolyte bath may be expressed in terms ofequivalent activity which these compounds display on weight basis underidentical conditions to ethylene diamine tetraacetate. Consequently,specifying an equivalent activity of a sequestering agent in terms ofethylene diamine tetraacetate also defines the amount of thesequestering agent.

As mentioned before, the bath is maintained at a pH from 5.5 to 8, thusthe above potassium phosphate and/ or potassium citrate are employed toobtain the desired pH conditions. In respect to the ranges for theactive components, gold in the form as defined above is used rangingfrom 10 to 15 grams per liter or more particularly 10.7 to 14 grams perliter or 1.3 to 1.5 troy ounce per gallon, and these are the desiredranges, with the preferred amount being about 12.3 g./l. Arsenic isdesirably used ranging from 0.02 to 0.04 gram per liter or 0.0026 to0.0052 ounce per gallon, preferably about 0.03 g./l. As the electrolytesalt composition, the above designated composition is representative,however, without reference to the unit volume of water. Further, theelectrolyte salt composition, as a combination, in its broadest genericaspect consists of gold in the form of a gold cyanide, arsenic and thecomplexing agent for the arsenic as listed in Table 1 above, againwithout reference to the unit volume of water. In a more narrow sense,the salt composition contains gold in the form of a gold cyanide, e.g.potassium gold cyanide, arsenic such as sodium arsenite, one of therecited complexing agents for arsenic added in an excess to thestoichiometric requirement for complexing arsenic in order to suppressarsine and to assure that no arsine escapes from the bath, a bufferingagent, e.g. potassium phosphate and/or potassium citrate to obtain therange of pH mentioned above when the salt is compounded to be dissolvedin some unit measure in a unit volume of water.

The potassium phosphate and/or potassium citrate mentioned above mayalso be added to give an approximate pH when the above-recited saltcomposition is added to water, and the final adjustment may be made byappropriate addition of the buffering agent. In the narrowest sense thesalt composition consists essentially of all the above-recitedcomponents and, in addition, for suppression of impurities asequestering agent such as disoduim ethylene diamine tetraacetatedihydrate. As it can be appreciated, a sequestering agent is added tosafeguard the formed deposit from inclusion of unwanted,impurityoriginated co-deposits during the deposition process. Hence, forpurposes of compounding the precursor salts for the electrolytesolution, a compounder may include the essential salts and any othersalts recited above or give directions on how the salts may besupplemented to produce the necessary electrolyte solution.

In operating an electrolyte bath, it has been found that temperatureranging from F. to F. can be usefully employed. An optimum temperatureis 140 F. If lower temperatures are used, then it has been found thatthe brightness of the heavy deposits decrease without loss of hardnessand etficiency. Thus, at a temperaure of 80 F. the deposits becomesofter (about 155, Knoop hardness number) and burnt. As the presentelectrolyte bath is of the so-called neutral bath type previouslydiscussed above, a conveniently suitable pH range is from 6.0 to 6.5. ApH of 6.2 represents the optimum condition. Specific gravity of thisbath is at least 10 B. The sodium (thiosulfate)-As (III) complex isreplenished in the electrolyte bath by adding a solution of 100 g./l. ofsodium thio-sulfate ('Na S- O -5H O) and 17.4 g./l. of sodium arsenite(NaAsO and bringing up the bath to the specified electrolyte compositionat the specified pH conditions, the last most conveniently by means ofthe buffering agent (although the addition of potassium gold cyanidewill affect the pH, the adjustment of pH is most conveniently achievedwith the buffering agents).

As the non-consumed anode material, carbon or platinum is used. Equallyinert materials may 'be also employed.

According to the invention, rack, basket, strip or selective platingmethods are suitable for obtaining the novel gold form. The use of astrike is recommended, since the electrolyte bath will immersion depositgold on nickel, copper or brass in less than one minute.

The above-described gold is commonly deposited on a metal base. Metalssuitable for this purpose and also useful as electrical conductors aresuch as copper and its alloys, iron and its alloys, nickel and itsalloys, aluminum and its alloys, etc.

Current density for a conventional rack plating method is up to about 10amperes per square foot (a.s.f.); at higher current densities in a rackplating method, the grain structure may change.

At a rack current density of 5 a.s.f. heavy deposits are dull, and at 15a.s.f. heavy deposits are burnt; there is negligible change inefficiency or hardness of the deposit. For a barrel plating method,current density is about 3 a.s.f. Higher current densities areobtainable when plating methods other than rack and barrel methods areemployed, e.g. up to 100 a.s.f. and higher if the previously mentionedarsenic complex formers, which also function as arsine suppressants, areemployed in the bath.

Agitation of the bath during the plating operation is carried out bymechanical means in a vigorous fashion.

The density of the deposit obtained, when employing a bath solution ofthe composition given in Table I, was 19.0 grams per cubic centimeter or31.2 milligrams per 0.0001 cubic inch. A hardness of to 250 Knoophardness units with a 25-gram load was obtained.

In the gold depositing art, the surface appearance of a deposit isclassified commonly as either bright, semibright, or matte. Inaccordance with this invention, rack plating work is bright to athickness of at least 1.5 mils, while barrel plated work is bright to athickness of at least 0.2 mil.

As mentioned before, the novel method of operating a bath ischaracterized by excellent efiiciency either on percentage basis ordeposition rates. Representative efficiency figures for the electrolytebath of the above composition are illustrated below:

The efiiciency in percent is defined as the amount of gold deposited incomparison with the theoretical efiiciency for pure gold which is 123mg./ amp minute.

When leaf type electrical connector articles were plated in the samebath, a plating rate to achieve 0.1 mil deposition was achieved in arack plating method in 3.6 to 4.0 minutes at 10 a.s.f. at theabove-identified optimum conditions while vigorously stirring theelectrolyte bath by mechanical means; in barrel plating, the same ratefor the same deposit thickness at 3 a.s.f. was achieved in 14.5 tominutes.

Electrical devices which can be suitably electroplated with the novelgold composition according to a method disclosed herein are items suchas crimpable or solderable electrical conductor, a coaxial connector,microminiature connections for integrated circuits, solid state devices,etc.

The structure of the novel gold deposit changes when certain impuritiesare found in the electrolyte. For example, copper, iron and nickel arecommonly encountered impurities. While copper, iron and nickel as animpurity(ies) do not adversely affect bath etiiciency or properties ofthe deposit, iron does effect a change in the crystalline structure ofthe deposit at levels as low as 10 mg./l. of electrolyte solution. Atthis concentration, the structure may be partially of randomly finecrystals and partially of columnar crystals. Further, while copper andnickel at low current density values, i.e. when rack plating at 5a.s.f., and concentrations up to 100 mg./l., do not change thecrystalline structure and properties at high current density values,e.g. at 10 a.s.f. or above, the struct-ure may be laminar for copper orcolumnar for nickel. These observations were made when plating with thecomposition in Table I at 140 F. and at 10 a.s.f. However, theseimpurities do not reduce gold from the electrolyte bath at the operatingconditions.

For high speed plating operation, the following electrolyte compositionhas been found to be very suitable. Composition and operating conditionsof an electrolyte bath and properties of the gold deposit areillustrated below.

TABLE IIL-ELECTROLYTE COMPOSITION, OPERATING CONDITIONS AND PROPERTIESOF ELECTRO DEPOS- I'IED GOLD IN A HIGH SPEED PLATING OPERATION SpecificComponents and conditions bath Suitable range Gold AsKAu(CN)1 31.1 g./l.Monobasie potassium phosphate 90 g./l 60 to 240. Potassium citrate 90g./l 60 to 240.

From lsltolehzigiat-I met 0 to gig thiosulfate m -flitg l poun o e e-Arsenic al mental arsenic by weight. pH of electrolyte- 6.2 5.5 to 8.Specific gravity 19 Be- Temp, F 140 100 to 160. Density, g./ec. ofdeposit. 18.5-.-- Cathode e11, percent- 88 Current density, a.s.fPlating rate (min.) .000 Knoop Hardness HK (25 g. load) Appearance Wt.percent As in deposit l3 l Each salt or mixture 01 same to assure a pHfrom 5.5 to 8.

In summary, as it is evident from the above discussion and data, theproportions of components in the electrolyte solution for high speed andrack and barrel plating range from 10 to about 32 grams per liter gold;arsenic from 0.02 to .2 gram per liter, the thio complexing agent fromstoichiometric ratio to a 250 or even 400 fold excess, on weight basis,the thio compound to elemental arsenic; and the buffering agent ormixtures of same from 60 to 240 grams per liter and suflicient to impartthe desired pH in the range from 5.5 to 8.

The above-described properties of the novel gold form were determinedaccording to the procedures for gold plated products set out inASTM-B4886S.

The term an electro deposited gold article is meant to cover both anelectroplated article and an electroformed gold article of which thelatter is an article which is built up to the desired dimensions by golddeposition from an electrolyte. The term a heavy gold deposit signifiesdeposited gold of a thickness in excess of one mil. In reference to arack plating method, high current density signifies values above 10a.s.f., i.e., up to 50 a.s.f. A low-stress gold deposit is definedherein as being ductile according to the ASTM test indicated above; andwherein an electro deposited gold foil, when removed from a base metalupon dissolution of the base is characterized by absence of failure bybending and unbending over a 0.32 dia. wire through 180 angular degrees.

What is claimed is:

1. An aqueous electrolyte solution for depositing hard and brightarsenic containing gold, said solution having a pH range from 5.5 to 8,comprising an alkali metal containing butter for imparting said pH rangeto said solution, an alkali metal gold cyanide complex, and a tris (thiosulfato) arsenic (III) complex or thio arsenic (III) complex to hardenand brighten the gold by inclusion of arsenic in a gold deposit.

2. An aqueous electrolyte solution according to claim 1 and wherein thetris (thio sulfato) arsenic (III) complex is derived from sodiumarsenite and sodium thio sulfate.

3. An aqueous electrolyte solution for electrolytic deposition ofarsenic gold from a dissolved electrolyte in a water medium, saidsolution comprising: as a buffering agent, monobasic potassiumphosphate, potassium citrate, or mixtures of same; an arsenic complexadded to said solution as sodium arsenite and sodium thio sulfate toyield 0.02 g./1iter of solution to .2 g./liter of solution of elementalarsenic in a ratio of said thio compound to elemental arsenic of up to250 fold excess; elemental gold, added as [KAu(CN) from 10 g./liter ofsolution to 32 g./liter of solution, the pH of said aqueous solutionbeing in the range from 5.5 to 8 imparted thereto by said bufferingagent and whereby an arsenic gold having from .1 to 1% by Weight ofarsenic in said gold deposition is obtained from said electrolytesolution under electro deposition conditions.

4. An electrolyte solution according to claim 3 and wherein the solutioncomprises on basis of one liter of water:

Grams Monobasic potassium phosphate or potassium citrate as K C H O .H Oor mixtures of said phosphate and citrate 60 to Arsenic complex:

Arsenic, as elemental arsenic and added as sodium arsenite .02 to .04Sodium thiosulfate, as Na S O .5H O 2 to 8 Elemental gold, added as[KAu(CN) 10 to 15 and wherein the pH of the solution is from 6.0 to 6.5imparted thereto by said phosphate or citrate, or mixtures thereof.

5. An electrolyte solution according to claim 4 and wherein asequestering agent is included in an amount based upon equivalentactivity of .25 g./liter of solution of dissodium ethylenediaminetetraacetate.

6. An aqueous electrolyte according to claim 3 and including asequestering agent based on equivalent activity of about .25 g./l. ofdissodium ethylenediamine tetraacetate dihydrate.

7. An aqueous electrolyte soltuion according to claim 3 suitable as ahigh speed plating electrolyte and wherein the solution comprises:

and wherein the solution upon palting on a metallic base is to yield agold deposit containing at least 0.1% to 1% by weight of arsenic.

8. An electrolyte solution according to claim 3 and wherein saidsolution contains trace amounts of metallic impurities.

9. A salt composition suitable for deposition of gold from anelectrolyzed aqueous solution thereof comprising: gold as potassium goldcyanide; arsenic as a trivalent arsenic compound; and as a complexingagent for said arsenic, an alkali metal thio sulfate.

10. A salt composition suitable for deposition of gold from anelectrolyzed aqueous solution of said salt composition at a pH from 5.5to 8, said salt composition comprising: monobasic potassium phosphate,potassium citrate, or mixtures of same; gold as [KAu(CN) arsenic assodium arsenite; and an alkali metal thio sulfate as a complexing agentfor said arsenic and as an arsine suppressant.

11. The salt composition according to claim 10 comprising: 60 g. ofmonobasic potassium phosphate; 60 g. of potassium citrate monohydrate;from 10 to 15 g. of gold on elemental basis as potassium gold cyanide; 5g. of sodium thio sulfate as sodium thio sulfate pentahydrate; and from0.02 g. to 0.04 g. of elemental arsenic as sodium arsenite.

12. The salt composition according to claim 11 and including .25 g. ofdissodium ethylene diamine tetraacetate dihydrate.

13. The salt composition according to claim and including as asequestering agent ethylene diamine tetraacetate dihydrate.

14. A method for depositing a hard, ductile and bright electro depositedgold ha-ving incorporated therein arsenic comprising the steps of:

introducing into an aqueous electrolyte solution a base coupled to acathode, said electrolyte being a buifered solution of potassiumphosphate, potassium citrate or mixtures of same as a bulfering agentand comprising an alkali metal gold cyanide complex having from 10 to 32g./liter of solution gold expressed as elemental gold, a tris(thio-sulfato) arsenic (III) complex, a thio arsenic (IH) complex, or amixture of said complexes including an excess of the thio compound andwherein said thio compound is up to a 400 fold by weight on basis ofelemental arsenic, said electrolyte solution being maintained at a pHfrom 5.5 to 8;

impressing a voltage between said cathode and an anode to obtain acurrent therebetween; and

depositing, at a temperature up to 160 F. on said base from theelectrolyte solution, arsenic and gold wherein said gold contains from.1% to 1% of arsenic to form a hard, bright and ductile gold deposit.

15. A method for depositing arsenic containing gold according to claim14 and wherein said electrolyte comprises on basis of one liter ofwater:

Grams As a buffering agent:

Monobasic potassium phosphate 60 to 120 Potassium citrate as K C H O -H'O 60 to 120 Arsenic complex:

Arsenic, as elemental arsenic and added as sodium arsenite .02 to .04Sodium thiosulfate, as Na S O -5H O 5 to 8 Elemental gold, added as[KAu(CN) 10 to 15 and wherein the pH of the solution is from 6.0 to 6.5imparted thereto by said buffering agent or mixtures of same.

16. The method for depositing gold according to claim 15 and wherein asequestering agent is used to safeguard against trace impurities.

17. The methodaccording to claim 15 and wherein a sequestering agent isused to safeguard against incorporation of trace amounts of metallicimpurities, said sequestering agent being used in an amount equivalentto, in activity, on a one liter basis of the solution of .25 g./liter,of the same solution of disodium ethylene diamine tetraacetatedihydrate.

18. A method for depositing arsenic containing gold according to claim14 and wherein said electrolyte is for high speed belt plating andcomprises:

Elemental gold, added as [KAu(CN) 31.1

Monobasic potassium phosphate Potassium citrate 90 Arsenic complex as:

Elemental arsenic added as sodium arsenite .10

Sodium thio sulfate as arsenic complexing agent 10 and wherein thesolution for said belt plating is to yield a gold deposit containing0.1% to 1% by weight of arsenic.

19. The method according to claim 18 and wherein as a sequestering agentethylene diamine tetracetate is used.

20. A method for depositing arsenic containing gold according to claim14 wherein the arsenic complex is derived from an arsenic compound andsodium thio sulfate, thio urea, or thio chrysine.

21. A method for depositing arsenic containing gold according to claim20 wherein the arsenic complex is formed in situ and wherein the arsenicis introduced as sodium arsenite.

22. A method for depositing gold according to claim 14 and wherein saidelectrolyte solution comprises: as a buffering agent, monobasicpotassium phosphate, potassium citrate or mixtures of same; an arseniccomplex added to said solution as sodium arsenite and sodium thiosulfate to yield 0.02 g./liter of solution to .70 g./ liter of solutionof elemental arsenic; elemental gold, added as KAu(CN) in an amount from10 g./l. to 32 g./l. of solution, the pH of said aqueous solution beingin the range of 5.5 to 8 and the deposited gold having from .1 to 1% byweight of arsenic in said gold.

23. The method for depositing arsenic containing gold according to claim14 and wherein said aqueous electrolyte comprises:

Elemental gold, added as [KAu(CN)2] 31.1 Arsenic complex, as:

Elemental arsenic, added as sodium arsenite .10

Sodium thio sulfate 10 24. A method for depositing arsenic containinggold according to claim 14 and wherein a 250 fold excess by weight ofsodium thio sulfate in reference to elemental arsenic is used as anarsine suppressing agent.

11 25. An aqueous electrolyte solution for depositing hard and brightarsenic containing gold, said solution comprising:

G./l. Monobasic potassium phosphate 60 Potassium citrate 60 Gold aspotassium gold cyanide 10.7 to 14 Arsenic as sodium arsenite .2 to .4

As complexing agent for said arsenite, sodium thiosulfate Elementalgold, added as [KAu(CN) 31.1

Potassium citrate 90 Monobasic potassium phosphate 90 Arsenic complexas:

Elemental arsenic added as sodium arsenite .10

Sodium thio sulfate as arsenic complexing agent impressing a voltagebetween said cathode and a nonconsumable anode to obtain a currenttherebetween; and

depositing, at a temperature up to 160 F. on the metal base from theelectrolyte solution, arsenic and gold to form a hard, bright andductile gold deposit.

27. An aqueous electrolyte solution for depositing hard and brightarsenic containing gold, said solution having a pH range from 5.5 to 8,comprising an alkali metal containing buffer for imparting said pH rangeto said solution, an alkali metal gold cyanide complex, and a tris(thio-sulfato) arsenic (HI) complex or thio arsenic (III) complex toharden and brighten the gold by inclusion of arsenic in a gold deposit,wherein the arsenic complex is derived from an arsenic compound andsodium thio sulfate, thio urea, or thio chrysine.

28. A salt composition suitable for deposition of gold from anelectrolyzed aqueous solution thereof comprising: gold as potassium goldcyanide; arsenic as a trivalent arsenic compound; and as a complexingagent for said arsenic, thio urea, thio chrysine, or sodium thiosulfate.

References Cited UNITED STATES PATENTS 3,666,640 5/1972 Smith 204-43 X3,423,295 1/1969 Greenspan 204-43 3,475,292 10/1969 Shoushanian 204-43 X3,520,785 7/1970 Duva 20443 GERALD L. KAPLAN, Primary Examiner US. Cl.X.R.

